1. Field of the Invention
This invention relates to a phase shifting mirror for creating a desired phase difference between the P-polarization reflected component and the S-polarization reflected component of a reflected light beam.
2. Description of the Prior Art
A phenomenon is known that when a light beam is reflected by the surface of a certain substance, a phase difference is created between a P-polarization reflected component and an S-polarization reflected component. For example, when a light beam is reflected by the outer surface of a dielectric material, a phase difference .pi. is created between the P-polarization reflected component and the S-polarization reflected component if the angle of incidence is smaller than the Brewster's angle.
In the metals generally used for a mirror, namely, aluminum, silver, chromium, etc., when a light beam is reflected by the surface thereof, a phase difference of approximately (.pi./2) is created between the P-polarization component and the S-polarization component. In this case, the angle of incidence at which the light beam is incident on the metal surface is about 45.degree., which is usually a standard value when the metal is used as a mirror.
Further, when a light beam is reflected by the surface of a mirror comprising a layer of dielectric material provided on the metal layer and having a film thickness of 1/4 of the design wavelength or a film thickness of a value which is an integer times as great as that, a phase difference of approximately (.pi./2) is created between the P-polarization component and the S-polarization component. Thus, in the mirror of such conventional surface reflection type, a phase difference of approximately .pi. is obtained between the P-polarization component and the S-polarization component during reflection, but if a phase difference substantially different from .pi. is to be obtained, the refractive index chiefly of the external medium and the refractive index of the substance which reflects the light beam must be varied. However, a substance corresponding to the refractive index of the substance obtained in calculation does not exist in the natural world.